There’s a new study of cancer and exercise that’s just been reported at a cancer conference in the USA and published in a major scientific journal, and which has made it to the media. It’s good news; and actually real good news.
The study finds that exercise actually improves survival in colon cancer. More precisely, it finds that providing an exercise coach improves survival compared to just providing the usual “exercise good; junk food bad” information. Obviously this wasn’t a double-blind trial — you can’t make people exercise without them knowing — but it measured objective health outcomes. In particular, the medical profession can measure death very reliably.
There have been lots of papers in the past showing that exercise is correlated with better health in people with colon cancer. The correlation is robustly unsurprising: the less well you are, the less you are able to exercise, and there was no way to be confident anything more than this was going on. This study was different, because people were randomly assigned to higher or lower pressure to exercise. It’s pretty unusual to have a study that actually changes people’s level of exercise over a long period, and even more unusual to show that it actually improves their health. We don’t know if the effect translates to other cancers — previous studies have had hypotheses about mechanisms that are specific to colorectal cancer and others that aren’t.
Since this is StatsChat, I do want to compare what the research paper and the news said about the size of the effect. Here’s the graph from the research paper
At the planned 8-year follow-up point, the difference in survival was 7 percentage points. Basically the same was true at the planned 5-year point for survival cancer-free. The overall survival difference narrowed a bit if you took the data out to ten years, and the cancer-free survival widened a bit. You could also quote the average ratio of the death rates (or cancer recurrence rates) in the two groups, which is common in the statistical analysis of cancer but is a bit harder to translate into real-world impact (and which gives much bigger numbers 28% or 36% reduction)
The Guardian just reported the relative rates. The BBC reported both, very clearly. Ars Technica reported both, but didn’t link the absolute and relative numbers as clearly as the BBC.
The Guardian also made a lot of the “better than a drug” comment by the chief medical officer of the American Society for Clinical Oncology,
“It’s the same magnitude of benefit of many drugs that get approved for this kind of magnitude of benefit – 28% decreased risk of occurrence, 37% decreased risk of death. Drugs get approved for less than that, and they’re expensive and they’re toxic.”
I think it’s worth noting that this is not saying exercise is better than chemotherapy. It’s saying exercise plus chemotherapy is better than chemotherapy along, and the margin is large enough that if it were new drug+chemo vs chemo alone you’d easily get approval.
